A polyimide film has been extensively used in the fields of electric/electronic devices, semiconductors and so on, because of its excellent heat resistance, chemical resistance, mechanical strength, electric properties, dimensional stability and so on. For example, for a flexible printed circuit board (FPC), there has been used a copper-clad laminated substrate where a copper foil is laminated on one or both sides of a polyimide film.
In general, a polyimide film may not, however, provide a laminate having adequately high peeling strength when a metal layer is formed on a polyimide film by dry plating such as metal deposition and sputtering, or when a metal layer is formed on a polyimide film by wet plating such as electroless plating.
In recent years, there has been investigated plastic substrates that are light and flexible as a replacement of a glass substrate in a field of optical materials, for example, a display field, and therefore optical materials having higher performance have been demanded. For example, methods of expressing transparency by using semi-alicyclic or wholly alicyclic polyimide resins are proposed (Patent Documents 1 to 3). For example, semi-alicyclic polyimides prepared using trans-1,4-diaminocyclohexanes as a diamine component and 3,3′,4,4′-biphenyltetracarboxylic dianhydrides as a tetracarboxylic acid component are known (Patent Document 3).
Patent Document 4 has described a polyimide from a triazine-based diamine, showing an example in which a polyimide solution is applied on a metal foil. In addition, as examples of the use of a triazine-based diamine, Patent Document 5 has disclosed an end-modified imide oligomer using a triazine-based diamine and Patent Document 6 has disclosed a polymer electrolyte using a triazine-based diamine. Patent Document 7 discloses a polyimide which uses a triazine-based diamine having two amino groups (—NH2) in para-positions in benzene rings relative to two NH groups bonded to the triazine rings (hereinafter, it may be referred as “p-ATDA”).